To reach your potential as a cyclist, it's a great idea to train with a power meter, and the Quarq ELSA brings together incredible accuracy and superb performance in a wireless, crank-based unit. It uses ANT+ wireless technology to pair with a head unit of your choice (sold separately), to display and record your data. Plus, an LED indicator lets you know you've correctly synced the ELSA with your head unit. And, the user-replaceable battery is a simple to swap and readily available CR2032. With the ELSA's excellent accuracy you get great data, even if you swap chainrings, thanks to Quarq's Omnical technology, and with their Power Balance, the ELSA also uses algorithms to determine the independent power from each of your legs, on the fly. Plus, the SRAM-made Exogram hollow carbon crankarms and precision-shifting 5-bolt chainrings will leave you floored by their lightness, stiffness and beauty.